Asperaxis karenae, Alderslade, 2006

Alderslade, Philip, 2006, New subfamilies and a new genus and species of Melithaeidae (Coelenterata: Octocorallia: Alcyonacea) with comparative data on the structure of both melithaeid and subergorgiid axes, Zootaxa 1199, pp. 19-47 : 23-47

Asperaxis karenae new species ( Figs 1–15 )

Material examined. Holotype: NTM C14986, Mundy Island , Bathurst Channel, Port Davey, Tasmania, Australia, depth 4–6 m, K. Gowlett­Holmes, 13 April 2002.

Paratypes: NTM C13575, same data as holotype ; NTM C14987, Sarah Island , Bathurst Channel, Port Davey, depth 8 m, G. Edgar, 20 March 1998 ; SAM H1397 , Sarah Island , Bathurst Channel, Port Davey, depth 5–12 m, rock slope to mud bottom, WEB station 1, K. Gowlett­Holmes, W. Zeidler, F.A. Bavendam, 3 April 1993 ; SAM H1398 , Schooner Cove , off Forrester Point , Bathurst Channel, Port Davey, steep wall, mud bottom, depth 3–18 m, WEB station 2, K. Gowlett­Holmes, W. Zeidler, F.A. Bavendam, 2 April 1993 ; SAM H1399 , same data ; SAM H1400 , Cathedral Cave , Waterfall Bay , Tasman Peninsula, Tasmania, depth 15–18 m, growing over phidoloporid bryozoan on rock wall, K. Gowlett­Holmes, 29 October 1994 ; SAM H1401 , Patersons Arch , Waterfall Bay, Tasman Peninsular, depth 10–13 m, on rock wall, K. Gowlett­Holmes, 17 September 1995 .

Description. The holotype is a fragile, bushy, rather sparsely branched, 60 mm high colony ( Figs 1–2A ). The very short, slightly flattened main stem is of uneven thickness with broadest diameter of 4.4 mm. It arises from a small 13 x 6 mm holdfast and immediately divides into two major branches, 2.2 mm and 2.4 mm in diameter respectively. One of these gives rise to a lateral branch that is overgrown by sponge for most of its length.

Branching in the colony is irregularly lateral to the third order, with terminal twig lengths varying from about 5–35 mm in length and 0.75–1.6 mm diameter. Nearly every twig terminates in a cluster of polyps ( Fig. 2A, B ). Branching may arise at an acute angle or is more or less perpendicular, and the branches are sinuous.

The axis consists of hard calcareous internodes and softer organic nodes, both of which incorporate sclerites ( Figs 2C , 3 ). The internodes are formed from sclerites wholly or partially embedded in a matrix of subhedral calcite rods ( Fig. 5 ). In some portions of the internodes, apparent imperfect or ongoing infilling with calcareous matrix has left the axis penetrated by numerous holes or canals. The internodal sclerites are mostly stick­ like, sparsely tuberculated, often sinuous and often branched ( Fig. 11A ) (and coenenchy­ mal sclerites are occasional included; see Fig. 6 Ea). On the outside of the internode they are partially embedded, commonly anastomosing and usually gathered into longitudinal ridges although they may cover much of or all the surface (compare Figs 3 & 9A ). Large longitudinal canals run through the coenenchyme between the axial ridges, as can be seen in the thick, partially decalcified section in Fig. 4B . The interior of the internode is partly hollow and contains a 3­dimensional latticework of anastomosing tuberculate spindles that is penetrated by mesogloea ( Figs 4A ; 9C,D ). Figure 5A depicts a longitudinal section through part of an internode, clearly showing part of the core lattice. The presence of embedded sclerites in the solid parts of the axis are not obvious from this aspect, as can be seen in the close­up ( Fig. 5C ), because the calcite rods from which they are constructed blend so well with those of the matrix. They can, however, easily be seen in a cross­sectional view, as depicted in Figure 9E, F .

Internodes begin in the tips of terminal twigs as an aggregation of both free and anastomosed sclerites. Infilling of the axis with the calcite matrix increases proximally. A growing terminal internode of a paratype is shown in Fig. 6A . The actual tip of this sample collapsed during processing with sodium hypochlorite to remove the coenenchyme. Figure 6F shows the tip of another twig axis processed for less time; the tuberculate spindles in the centre ( Fig. 6 Fa) were presumably destined to be incorporated into the trabecular core of the internode. Figure 6D shows the cavity left where a small partial node has been dissolved.

Nodes may be whole (ie. completely divide a branch portion into separate internodes as in Figs 3B ; 7E ) or they may be partial. Partial nodes vary from those that almost completely separate internodes to those that are exceedingly small and inset into the side of an internode ( Figs 3C ; 6D ; 7 A–D). There is no distinct boundary between nodes and internodes. At the juncture, the end of the internode consists of an irregular arrangement of partially embedded, protruding sclerites between which the nodal material has been deposited; figure 9B shows a very short, complete internode. Partial nodes are similar in that the solid internodal material gives way to partially embedded sclerites ( Fig. 7A,B ). Nodal sclerites appear to be the same as the stick­like internodal forms with the addition of short rods with thickened tuberculate ends ( Fig. 7D ). On the node surface these sclerites are often seen to been aggregated in such a way as to form continuations of the internodal sclerite ridges, and some anastomoses may occur; see Fig. 3B (whole internode) and Fig. 3C (partial internode). Within the node, sclerites are held in an organic matrix. The sclerites are sheathed in gorgonin, which binds them together leaving interconnected cavities containing mesogloea ( Fig. 8 A–C).

Branches arise from large, whole or partial nodes that are mostly inconspicuous (especially on thin branches) as they are commonly more or less the same thickness as the adjoining internodes. Nodes are also present in non­branching sections, and there may be a number of them crowded between points of bifurcation. They can be slightly swollen relative to the internodes, but this may not be reflected in a notable increase in branch thickness unless on thick basal branches. Internode length is estimated to vary from 0.75– 10.00 mm, and nodes can be at least 1.5 mm long. The range of length of axial segments is difficult to accurately ascertain because the process is destructive.

One of the reasons this colony has been selected as the holotype is that the polyps are slightly distended. The tentacles are folded over the mouth, and the polyp head generally sits just above the calyx ( Fig. 10A ). Polyps are scattered irregularly along the branches, either singly or in groups of 2 or 3, and are gathered in terminal clusters of 4–15 ( Fig. 2B ).

A few calyces are cylindrical but most are slightly expanded distally showing the contracted introvert between the rim and the polyp head. The largest calyx is 1.2 mm tall, 1.2 mm basal diameter, and 1.9 mm distal diameter. The largest polyp head is 1.2 mm tall and 2.0 mm across. Juvenile polyps occur here and there on branches, but are most commonly found in the terminal clusters where they can be as short as 0.4 mm.

The calicular sclerites are sticks, spindles, and clubs about 0.15–0.28 mm in length ( Fig. 12 ). The tubercles are mostly large, complex, and irregularly arranged. The sclerites are oriented longitudinally in the lower half of the calyx, becoming formed into 8 chevrons in the upper half, and forming 8 teeth on the calyx rim ( Fig. 10A ).

The polyp head is heavily armed with numerous point sclerites ( Fig. 10A ). At the base of each point the sclerites are more or less horizontally arranged and these combine with a small number of long bow­shaped sclerites to constitute a weak collaret. Above this region the sclerites are in chevrons, becoming longitudinal as they encroach on the base of each tentacle. Between each set of points there is a group of 2–7 (usually about 2) lower, intermediate, stick­like sclerites of various sizes, and above this there are 0–2 small, upper, intermediate sclerites ( Fig. 10B in­sc, 11B). The point sclerites are sticks and clubs. A few clubs ( Fig. 13 Aa) occur in the distal part of each of the points. They have large tuber­ cles and branched heads and are about 0.12–0.20 mm long. The remainders of the point sclerites are flattened sticks c. 0.07–0.29 mm long with simple tubercles ( Fig. 13 Ab). In the pharynx there are small rods about 0.036–0.066 mm long that have two medial girdles of knob­like tubercles ( Fig. 13B ).

Along each edge of the tentacles is a single row of about 10 pinnules that are ringed with nematocyst batteries ( Fig. 10 C–D). The aboral aspect of the tentacle is covered with two rows of transversely placed scales ( Figs 10B , 14A ) that are about 0.09–0.28 mm long. Proximally, the scales are crescent­shaped to fit the curvature of the tentacle surface and they are complexly branched or have branched tubercles. Distally the scales become shorter and simpler in design. On the adoral face there is a single small scale associated with the base of each pinnule ( Fig. 10B pi­sc, D). These scales are asymmetrical folia­ ceous crescents ( Fig. 14B ), 0.09–0.16 mm long and they lie curved around the proximal side of the pinnule base. The narrow tail of the scale seems to lie on the lateral edge of the tentacle rachis, the crescent curves around the pinnule base, and the foliaceous portion lies on the oral face of the pinnule base.

The sclerites of the twigs and branches are complexly tuberculated sticks and spindles, occasionally branched, 0.05–0.28 mm in length ( Fig. 15 ).

Colour. Live colonies are pale pink. Preserved colonies are white to pale brown with white internodes and pale yellow nodes.

Variability: Several of the paratype lots consist of colonies or colony fragments that are noticeably thinner than the holotype.

a) Polyp density can be quite variable, with some colonies having long branches with very few polyps

b) Clusters of polyps are very common, and do not only occur at the end of terminal branches.

3) Club­like sclerites may be few or even rare in the tip of the points arrangements.

4) Several lots show signs of initial preservation in acidic formalin.

Etymology. The species is named for my good friend and colleague Karen Gowlett­ Holmes, Marine Collection Manager, CSIRO Tasmania, and multi­award winning underwater photographer. Karen is a regularly donator of material to the MAGNT collected during her many private expeditions.

Remarks. The species is known from two types of habitat. The following comments are those of Karen Gowlett­Holmes:

“Both habitats are extremely low­light, and both have other taxa usually found in much deeper environments. In the Waterfall Bay caves, the low light is similar to about 50+ m deep, and much of the fauna is the same as that seen at this depth or deeper. The Bathurst Channel, on the other hand, appears to be an isolated water body with regards to the open ocean, and has a strong pycnocline across the mouth of the channel. The area is a drowned river valley, flooded sometime about 12,000 to 15,000 years ago, and it is likely that the current sessile fauna invaded the area at that time and has been virtually isolated for about 10,000 years. What makes the region most unusual is that the upper two to four metres of the water column is a distinct layer of virtually fresh, darkly tannin­stained water (like very strong black coffee). The transition into the marine layer below is very sharp and the marine layer is very clear and very dark. The fauna of the Bathurst Channel most closely resembles that of the shelf break and upper slope, for example 80 to> 120 m depth. I therefore think the new taxon is probably a deepwater emergent species. Further evidence for this is that the new taxon is always associated with various bryozoan species and these species are also known from deep water. It occurs predominantly with Triphyllozoon floribundum (Phidoloporidae) , a fenestrate bryozoan that forms small colonies in the caves but very large colonies (up to at least 60 cm in diameter) in deeper water and in the Bathurst Channel. Sometimes the gorgonian is found with Schizoretepora tesselata (Phidoloporidae) , a poorly known fenestrate species found in the caves and the Bathurst Channel, and occasionally dredged on the shelf break. Less commonly, the new gorgonian is found associated with Idmidronea sp. (Cyclostomata: Tubuliporidae ), an undescribed, finely branching, arborescent spe­ cies found in the caves, on rock walls, and common out to the shelf break. On one occasion the new gorgonian was found with Adeonellopsis sp. ( Adeonidae ), a pos­ sibly undescribed branching species that is one of the dominant species found on the outer shelf, shelf break, and upper slope, and is common in dark areas in the caves and in the Bathurst Channel.

Bryozoans in this part of the world are rarely overgrown by anything (at least for long), as they produce deterrent secondary metabolites and have other means of defence as well. It may be worth noting, therefore, that it is quite common to find small colonies of Mopsella zimmeri growing on Triphyllozoon munitum in South Australia, so perhaps some groups of melithaeids have an affinity with phidol­ oporids in particular.”

Comparative Comments. Although the axis of the new genus has obvious morphological differences to that found in a nominal melithaeid genus such as Acabaria or Melithaea , the basic constructional scheme is very similar.

One of the obvious differences is that in current nominal genera the node­internode articulation is relatively well defined. The node of a species of Acabaria is depicted in Fig. 16A . The overlying coenenchyme has been removed, revealing the typical melithaeid axial sclerites partially cemented together on the internodal surface ( Fig. 16B, C ) and forming a 3­dimensional meshwork in the node ( Fig. 16D ). An enlargement of the region where the hard internode material abuts the softer nodal substance is shown in part E of that figure. Across the centre of this image, part of a latticework can be seen where sclerites are anastomosing or linked by calcite bridges ( Fig. 16 Ea). If all the soft nodal material and loose sclerites are removed from the end of an internode, this latticework is shown to be covering its conoid end in a shallow layer ( Figs 17B, C ; 18D ). The sclerites in the rounded tip of the internode, however, are different ( Fig. 17 Aa). These are larger spindles with a number of rounded tubercles, somewhat similar to those that can be found in the axis that is forming in the tips of Asperaxis twigs, which presumably become incorporated into the latticework of the internodal core. The formative melithaeinid axis appears to be similar to that of Asperaxis . Figure 18A depicts a decorticated twig tip of a Melithaea species. As in Asperaxis , an internode begins as an aggregation of loosely bound tuberculate spindles ( Fig. 18 Ba), the rod­shaped sclerites by which the melithaeid axis has usually been characterised occurring only on the outside ( Fig. 18 Ab, Bb). Figure 18C shows the surface of an older internode; cavities are still present where the calcite infilling is not yet complete. In the early stages of sclerite fusion, an internode is mainly just a cylindrical latticework (the future core), with a layer of small, loose, rod­like sclerites on the outside ( Fig. 18E ). As the internode ages, the core becomes surrounded by large numbers of these rods embedded in a matrix of subhedral calcite rods ( Fig. 17 D–F). The core continues right into the tip of the conoid end of the internode ( Fig. 18D ) and, according to Koelliker (1865, pl. XV, fig. 8), the mesogloea of the core (his “Centralstrang”) is continuous from internode to internode through the node.

Axes from specimens having the characters of classical species of Melithaea , Mopsella , and Acabaria were examined in the course of this research and all were found to have the same basic construction. Additionally, because the sparsely tuberculate axial sclerites of Asperaxis (eg. Fig. 9A ) have similarities to those in the axes of Subergorgia and Annella , species of these genera were also examined. The axis of Annella reticulata ( Ellis & Solander, 1786) and that of Subergorgia suberosa ( Pallas, 1766) are illustrated in figures 19 and 20 respectively. The presence of free tuberculate sclerites in a subergorgiid axis (sclerites like those in the outer coenenchyme) is not well documented despite being discovered by Koelliker 140 years ago (1865, p. 144 and pl. XV, fig. 2). Indeed, it was overlooked by López­González and Gili (2001, p. 122), who used the presence of these sclerites in the axis of the new genus Rosgorgia as a major character distinguishing that genus from Annella and Subergorgia . Fabricius and Alderslade followed suit pending further investigation (2001, p. 56). In the several samples of Annella and Subergorgia that were analysed for this paper, tuberculate sclerites were commonly found in the centre of the axes, but they are not restricted to this region ( Figs 19B , 20B ). However, the simple, non­anastomosing spindles (with or without a few terminal tubercles) reported and figured by a few authors (eg. Aurivillius 1931, p. 21, fig 2 (centre); Bayer 1956, p. F198, 2c) do seem to be restricted to the centre of the axes ( Figs 19B,C , 20B,C ). At least in the few samples examined, this central section is certainly not composed solely of tuberculate coenenchymal­style sclerites as stated by Kinoshita (1910, p. 224–225) and seemingly implied by Muzik and Wainwright (1977, p. 321).

Acknowledgments

My thanks to Graham Edgar and Karen Gowlett­Holmes for donating specimens of the new taxon, and additionally to Karen for sharing her knowledge of the new taxon’s habitats and associations. Thanks also to Thierry Laperousaz for the loan of material from the South Australian Museum, and to Ellie Haywood, Charles Darwin University, for providing the Mallory­Heidenhain’s stain. I am also very grateful to my friends and colleagues Leen van Ofwegen (Nationaal Natuurhistorisch Museum, Leiden), Suzanne Horner (MAGNT), Gary Williams (California Academy of Sciences, San Francisco), and Manfred Grasshoff (Naturmuseum Senckenberg, Frankfurt) for critically reading the manuscript.

References

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Figures

FIGURE 1. Asperaxis karenae n. gen., n. sp., holotype NTM C14986 & paratype NTM C13575, in situ with a colony of the bryozoan Triphyllozoon floribundum (photo: K. Gowlett­Holmes).

FIGURE 2. Asperaxis karenae n. gen., n. sp., holotype: A, colony; B, polyps clustered on twig tip; C, light photograph of decorticated axis fragment.

FIGURE 3. Asperaxis karenae n. gen., n. sp., holotype, axis: A, internodes and nodes; B, close­up of a whole node; C, close up of a partial node; D, close up of part of an internode.

FIGURE 4. Asperaxis karenae n. gen., n. sp., holotype, decalcified twig cross­sections: A, intern­ ode region, showing mesogloeal remnants; B, partially decalcified section through internode region showing axis and longitudinal canals; C, nodal region with close­up showing gorgonin remnants.

FIGURE 5. Asperaxis karenae n. gen., n. sp., holotype, axis: A, longitudinal section through internode fragment; B, close­up of calcite matrix on internode surface; C, close up of calcite matrix from internode interior.

FIGURE 6. Asperaxis karenae n. gen., n. sp., developing axis: A–E, holotype; A, from distal portion of twig; B, close­up of region near tip; C–E, close­ups of older portions, with D showing cavity remaining from a dissolved partial node; F, paratype SAM H1398, axis tip.

FIGURE 7. Asperaxis karenae n. gen., n. sp., holotype: A–B, C–D, cavities left by dissolved partial nodes; E, branching node.

FIGURE 8. Asperaxis karenae n. gen., n. sp., paratypes: A–B, SAM H1400, cross section through node with close­up of nodal sclerites with gorgonin sheaths; C, NTM C14987, longitudinal section through a node showing nodal sclerites held within sheathing gorgonin.

FIGURE 9. Asperaxis karenae n. gen., n. sp., holotype: A, partially embedded internodal surface sclerites; B, complete internode; CD, internode cross­section with close­up featuring the central core; EF, internode cross­section featuring sections through embedded sclerites.

FIGURE 10. Asperaxis karenae n. gen., n. sp., holotype: A, polyp and calyx; B, side view of cleared tentacle, in­sc = intermediate sclerites, pi­sc = pinnule scales; C, tentacle tip showing nematocyst bands; D, tentacle tip showing position of pinnule scales.

FIGURE 11. Asperaxis karenae n. gen., n. sp., holotype: A, axial sclerites; B, points and collaret arrangement.

FIGURE 12. Asperaxis karenae n. gen., n. sp., holotype, calicular sclerites.

FIGURE 13. Asperaxis karenae n. gen., n. sp., holotype, anthocodial sclerites: A, points; B, pharynx.

FIGURE 14. Asperaxis karenae n. gen., n. sp., holotype, tentacular sclerites: A, rachis; B, base of pinnules.

FIGURE 15. Asperaxis karenae n. gen., n. sp., holotype, coenenchymal sclerites.

FIGURE 16. Acabaria sp. axis: A, decorticated node­internode articulation; B–C, serial close­ups of internode surface; D, close­up of nodal sclerite network showing sclerites with peeling gorgonin sheaths; E, close­up of internode­node boundary region showing the edge of the underlying fused latticework.

FIGURE 17. Acabaria sp. axial internodes: A–C, tip of internode with indicated close­ups; D–F, cross­section of internode showing cental core, and serial close­ups showing sections through embedded sclerites.

FIGURE 18. Melithaea sp. axial internodes: A–B, developing tip with associated close­up; C, surface of older internode; D, longitudinal section featuring central core and terminal latticework; E, longitudinal section through part of young internode almost wholly consisting of core structure.

FIGURE 19. Annella reticulata axis: A, anastomosed surface sclerites; B–C, longitudinal section with close­up of central region featuring free sclerites.

FIGURE 20. Subergorgia suberosa axis: A, anastomosed surface sclerites; B–C, longitudinal section with close­up of central region featuring free sclerites.